We have identified a new genetic locus in Escherichia coli, tentatively called rdg for recA dependent growth. This locus, near minute 16 of the current E. coli map, can be deleted in wild-type strains, but not in recA mutants. The following is proposed: a) Direct measurement of RNA synthesis following temperature shift of rdg recAts mutants to document our inference that RNA synthesis is the primary effect of the rdg mutation. b) Precise mapping of the rdg locus by co-transduction with nearby markers. c) Isolation of specialized transducing phages carrying rdg, or cloning the rdg gene on a convenient vector by in vitro methods. d) Identification of the rdg gene product. e) Development of an in vitro system to determine the precise function of the rdg product in macromolecular synthesis.